One of the known relay stations wirelessly transmits data received from multiple terminals to a wireless base station. In cases where the terminals are, for example, sensor devices that are not hold by users, the relay station is called a Machine-to-Machine GateWay (M2M GW). The wireless base station transmits the data received from the relay station to a server, which is connected to the wireless base station via a communication network. The server stores therein the data received from the wireless base station.
Each terminal detects a physical value each time a certain period elapses and transmits data representing the result of the detection to the relay station. Examples of the physical value are temperature, humidity, and a consumed amount of electricity. The data has a certain size. The transmission period and the size of data may be different with terminal. For example, one terminal transmits 40-byte data at a one-second period to the relay station while another terminal transmits 60-byte data at a two-second period. In this case, although each individual terminal transmits data of a constant size, the data size that multiple terminals transmit to the relay station fluctuates as the passage of time.
The following first through third wireless communication systems have been known (see, for example, Patent Literatures 1-3). In a first wireless communication system, the wireless base station notifies the relay station of setting information of logical paths that the relay station needs to communicate with the wireless base station and terminals. In a second wireless communication system, the relay station receives data destined for multiple terminals and mapping reference from the wireless base station. The relay station specifies a wireless resource between the relay station and each terminal on the basis of the mapping reference, and transmits data to each terminal using the specified wireless resource. In a third wireless communication system, a terminal transmits data to the wireless base station at a period that is determined on the basis of the state of a wireless channel of the terminal.
[Patent Literature 1] Japanese Laid-Open Patent Publication No. 2012-44336
[Patent Literature 2] Japanese National Publication No. 2010-532973
[Patent Literature 3] Japanese Laid-Open Patent Publication No. 2012-231263